FAMILY FRINGILLIDAE 



perch. Singing is closely tied to the advent of the wet season — during 

 the driest months of the year it is silent, but begins singing as soon as 

 the rains commence; singing is most vigorous during the months in 

 which it nests, but continues until the rains end many months later. 



TIARIS OLIVACEA PUSILLA Swainson 



Tiaris pusillus Swainson, 1827, Philos. Mag., new ser., 1, p. 438. (Tableland, 



Temascaltepec, and Real de Monte, Mexico.) 

 Tiaris olivacea dissita Thayer and Bangs, 1906, Bull. Mus. Comp. Zool., 46, p. 223. 



(savanna of Panama, Panama.) 



Characters. — Male, black restricted to forehead, sides of face to eye, 

 and throat and breast; green of upper surface lighter, more yellowish; 

 female more yellowish green throughout. 



A male collected at Las Palmitas, Los Santos, on January 26, 1962, 

 had the iris dark brown; bill fuscous-black; tarsus and toes brownish 

 neutral gray; claws dusky neutral gray. A female taken there the next 

 day had the iris dark brown; maxilla fuscous; sides and tip of mandi- 

 ble dull greenish gray; lower surface dull brownish white; tarsus, toes, 

 and claws dark neutral gray. 



Measurements. — Males (10 from Panama), wing 47.5-52.2 (50.4), 

 tail 36.2-44.8 (40.6), culmen from base 9.3-10.5 (9.8), tarsus 14.8- 

 16.5 (15.6) mm. 



Females (10 from Panama), wing 47.0-51.0 (49.0), tail 37.6-41.7 

 (39.4), culmen from base 9.0-10.8 (9.7, average of 9), tarsus 14.3-15.9 

 (15.4) mm. 



Resident. Very common in the foothills and highlands of both 

 slopes; scarcer and more local in the lowlands, more numerous on the 

 Pacific slope. In the Chiriqui highlands, I have found it as high as 

 1740 m at Cerro Punta, and Monniche collected it between 1560 and 

 1650 m on the Volcan de Chiriqui. 



The Yellow-faced Grassquit begins nesting later than most other 

 Panamanian birds because it waits until the rainy season produces a 

 new supply of grass seeds, its major food. Skutch (Pac. Coast. Avif. 

 no. 31, 1954, pp. 38-49), who has studied the nesting of this species in 

 Costa Rica, found no nests before April; in some years birds continued 

 to nest into January. Courtship includes a display in which the male 

 stands close to a female, sings, and vibrates his wings while facing her. 

 Both sexes assist in nest construction and the male defends a territory 

 of approximately 7 to 10 m around the nest. 



The nest is placed in a tussock of grass or a low bush and is an ovoid 



